1. Field of the Invention
The present invention relates to a power unit for a motorcycle, and particularly to a power unit suitable for a hybrid type motorcycle including an electric motor in addition to an engine.
2. Description of Related Art
Vehicles of the type using gasoline engines as a drive source are mainly available; however, vehicles of a type using an electric motor as a drive source are required at locations where occurrence of exhaust gas must be avoided. An electric motor-driven vehicle, however, is inconvenient, since it has increased body weight and shortened running distance. To cope with such an inconvenience, it has been increasingly required to develop a hybrid type vehicle including an electric motor in addition to an engine.
For example, Japanese Patent Laid-open No. Hei 8-175477 discloses a hybrid type motorcycle entitled "Device for switching Engine Power to/from Motor Power in Motorcycle or the Like".
As shown in FIG. 2 of the above document, an engine 10 is disposed in front of a rear wheel 37, with a cylinder of the engine 10 projecting forward or slightly obliquely forward.
According to the related art structure, as the cylinder of the engine becomes longer, the rear wheel 37 must be correspondingly shifted backward, to thereby extend the wheel base (distance between front and rear axles). The erection of the cylinder axis restricts space for a helmet containing box, e.g.